Base station, mobile station, wireless communications system, and wireless communications method

ABSTRACT

At a base station, a lookup table is prepared that for each index value among multiple different index values, associates repetition counts of different channels correlated with each other. The base station acquires reception information indicating a reception state of a wireless signal at a mobile station, determines a repetition count for each channel based on the reception information, and acquires from the lookup table, an index value corresponding to the respective repetition counts for the channels. The base station transmits to the mobile station, a wireless signal that includes the index value to notify the mobile station of the index value. The mobile station has a lookup table that for each index value among different index values, associates repetition counts of different channels correlated with each other and acquires the repetition counts of the channels from the lookup table, based on the index value from the base station.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of InternationalApplication PCT/JP2013/076154 filed on Sep. 26, 2013, and designatingthe U.S., the entire contents of which are incorporated herein byreference.

FIELD

The embodiments discussed herein are related to a base station, a mobilestation, a wireless communications system, and a wireless communicationsmethod.

BACKGROUND

In a conventional wireless network, control information is transmittedmultiple times so as to receive the control information under anenvironment with a low signal-to-noise ratio (SNR). Additionally, acommunications system exists that is called machine-to-machine (M2M) inwhich machines such as terminals communicate with each other ormachine-type communication (MTC) in which a machine and a server on anetwork communicate with each other (see, for example, PublishedJapanese-Translation of PCT Application, Publication Nos. 2012-522427,2013-524563, and 2013-520100).

For example, under an environment with a low signal-to-interference andnoise power ratio (SINR), transmission power may be increased (powerboost) or transmission may be repeated to expand coverage and maintain acommunication link between a base station and a mobile station. Iftransmission is repeated, the base station notifies the mobile stationof information necessary for signal reception such as a transmissionrepetition count.

However, a required transmission repetition count varies depending onthe transmission power of the base station and also varies depending onphysical channels, which have differing quality requirements. Therefore,the base station notifies the mobile station of information concerning apower offset amount for increasing the transmission power andinformation concerning the transmission repetition count for each of thephysical channels, resulting in a problem of increased information thatis to be notified.

SUMMARY

According to an aspect of an embodiment, a base station includes atransmitting circuit that transmits a first wireless signal to a mobilestation by using different physical channels; a receiving circuit thatreceives a second wireless signal transmitted from the mobile station;an acquiring circuit that acquires reception information indicating areception state of the first wireless signal at the mobile station, fromthe second wireless signal received by the receiving circuit; adetermining circuit that based on the reception information acquired bythe acquiring circuit, determines a repetition count of a third wirelesssignal repeatedly transmitted from the transmitting circuit; and alookup table that has an index value associated with repetition countsof the different physical channels. The base station uses the receivingcircuit to receive the second wireless signal that includes thereception information from the mobile station. The base station uses theacquiring circuit to acquire the reception information from the secondwireless signal that includes the reception information. The basestation uses the determining circuit to determine based on the receptioninformation, the repetition count for each physical channel among thedifferent physical channels. The base station acquires from the lookuptable, the index value that corresponds to the repetition counts of thedifferent physical channels. The base station uses the transmittingcircuit to transmit a fourth wireless signal that includes the indexvalue, to the mobile station and notify the mobile station of the indexvalue.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of an example of a wireless communications systemaccording to an embodiment;

FIG. 2 is a diagram of a functional configuration of a first example ofa base station according to the embodiment;

FIG. 3 is a diagram of a flow of signals or data in the base stationdepicted in FIG. 2;

FIG. 4 is a diagram of an example of a hardware configuration of thebase station according to the embodiment;

FIG. 5 is a diagram of an example of a wireless communications methodperformed by the base station according to the embodiment;

FIG. 6 is diagram of a functional configuration of a first example of amobile station according to the embodiment;

FIG. 7 is a diagram of a flow of signals or data in the mobile stationdepicted in FIG. 6;

FIG. 8 is a diagram of an example of a wireless communications methodperformed by the mobile station according to the embodiment;

FIG. 9 is a diagram of an example of maximum coupling loss betweenuplink and downlink;

FIG. 10 is a diagram of an example of a relation between repetitioncount and power boost for a required coverage expansion level;

FIG. 11 is a diagram of a functional configuration of a second exampleof the base station according to the embodiment;

FIG. 12 is a diagram of a flow of signals or data in the base stationdepicted in FIG. 11;

FIG. 13 is a diagram of an example of a lookup table;

FIG. 14 is a diagram of a functional configuration of a second exampleof the mobile station according to the embodiment;

FIG. 15 is a diagram of a flow of signals or data in the base stationdepicted in FIG. 14;

FIG. 16 is a diagram of an example of a wireless connection processsequence in a wireless communications system according to theembodiment;

FIG. 17 is a diagram of an example of a sequence of notification of anindex value common to channels; and

FIG. 18 is an example of a sequence of notification of respectiverepetition counts for the channels.

DESCRIPTION OF EMBODIMENTS

Embodiments of a base station, a mobile station, a wirelesscommunications system, and a wireless communications method according tothe present invention will be described in detail with reference to theaccompanying drawings. In the description of the embodimentshereinafter, identical components are given the same reference numeraland redundant description is omitted herein. Furthermore, the presentinvention is not limited by the following embodiments.

FIG. 1 is a diagram of an example of a wireless communications systemaccording to an embodiment. As depicted in FIG. 1, the wirelesscommunications system includes a base station 1 and a mobile station 2.

The base station 1 has a transmitting unit 11, a receiving unit 12, anacquiring unit 13, a determining unit 14, and a lookup table 15. Thetransmitting unit 11 is a base-station transmitting unit; the receivingunit 12 is a base-station receiving unit, the acquiring unit 13 is abase-station acquiring unit; and the lookup table 15 is a base-stationlookup table. The units 11 to 14 and the lookup table 15 of the basestation 1 will be described in detail in a first example of a basestation described later.

The mobile station 2 has a transmitting unit 21, a receiving unit 22, agenerating unit 23, an acquiring unit 24, and a lookup table 25. Thetransmitting unit 21 is a mobile-station transmitting unit; thereceiving unit 22 is a mobile-station receiving unit; the acquiring unit24 is a mobile-station acquiring unit; and the lookup table 25 is amobile-station lookup table. The units 21 to 24 and the lookup table 25of the mobile station 2 will be described in detail in a first exampleof a mobile station described later.

The base station 1 transmits a wireless reference signal to the mobilestation 2. The mobile station 2 receives the wireless reference signal,generates reception information indicating a reception state based onthe wireless reference signal, and transmits a wireless signal includingthe reception information to the base station 1. As a result, the basestation 1 is notified of the reception information.

The base station 1 receives the wireless signal that includes thereception information, acquires the reception information from thewireless signal, and for each physical channel among multiple differentphysical channels, determines a repetition count for a repeatedlytransmitted wireless signal, based on the reception information. Therepetition counts of the different physical channels correlate with eachother. Therefore, for each piece of reception information, therepetition counts of the different channels can be associated with oneindex value.

The base station 1 acquires from the lookup table 15 thereof, an indexvalue that corresponds to the respective repetition counts of thephysical channels and transmits a wireless signal including the indexvalue to the mobile station 2. As a result, the mobile station 2 isnotified of the index value.

The mobile station 2 receives the wireless signal that includes theindex value corresponding to the reception information reported by themobile station 2 and acquires the index value from the wireless signal.The mobile station 2, from the lookup table 25 thereof, acquires foreach physical channel, the repetition count corresponding to the indexvalue. As a result, the mobile station 2 can acquire the repetitioncounts of the different physical channels.

FIG. 2 is a diagram of a functional configuration of a first example ofthe base station according to the embodiment. FIG. 3 is a diagram of aflow of signals or data in the base station depicted in FIG. 2. Asdepicted in FIGS. 2 and 3, the base station 1 has the transmitting unit11, the receiving unit 12, the acquiring unit 13, the determining unit14, and the lookup table 15.

The transmitting unit 11 is connected to the lookup table 15 and anantenna 16. The transmitting unit 11 transmits from the antenna 16 tothe mobile station 2, wireless signals by using different physicalchannels. The transmitting unit 11 transmits the wireless referencesignal from the antenna 16 to the mobile station 2. The transmittingunit 11 transmits from the antenna 16 to the mobile station 2, awireless signal that includes an index value acquired from the lookuptable 15. As a result, the base station 1 notifies the mobile station 2of the index value.

The receiving unit 12 is connected to an antenna 17. The receiving unit12 receives wireless signals transmitted from the mobile station 2 viathe antenna 17.

The acquiring unit 13 is connected to the receiving unit 12. Theacquiring unit 13 acquires from the wireless signal received by thereceiving unit 12, the reception information indicating a receptionstate of a wireless signal at the mobile station 2. Based on thereception information acquired by the acquiring unit 13, the determiningunit 14 determines for the respective physical channels, the repetitioncounts for wireless signals repeatedly transmitted from the transmittingunit 11.

In the lookup table 15, different index values are respectivelyassociated with the repetition counts of the different physicalchannels. From the lookup table 15, index values are obtained thatcorrespond to the repetition counts determined by the determining unit14 for the different physical channels.

FIG. 4 is a diagram of an example of a hardware configuration of thebase station according to the embodiment. As depicted in FIG. 4, thebase station 1 has a processor 101, memory 102, and an interface 103.The processor 101, the memory 102, and the interface 103 may beconnected to a bus 104.

The processor 101 processes a program implementing a wirelesscommunications method performed by a base station described later. Theacquiring unit 13 and the determining unit 14 may be implemented in thisway at the base station 1 depicted in FIG. 2. Examples of the processor101 include a central processing unit (CPU), a digital signal processor(DSP), an application specific integrated circuit (ASIC), and aprogrammable logic device such as a field programmable gate array(FPGA).

The memory 102 retains the lookup table 15. The memory 102 stores a bootprogram and the program implementing the wireless communications methodperformed by the base station described later. If the processor 101 is aprogrammable logic device, the memory 102 may store circuit informationof the programmable logic device.

The lookup table 15, various programs, or the circuit information may bestored in a non-volatile area of the memory 102. The non-volatile areaof the memory 102 may be implemented by, for example, read only memory(ROM) such as mask ROM, electrically erasable programmable read onlymemory (EEPROM), and flash memory.

In the memory 102, a volatile area may be used as a work area of theprocessor 101. The volatile area of the memory 102 may be implementedby, for example, random access memory (RAM) such as dynamic randomaccess memory (DRAM) and static random access memory (SRAM).

The interface 103 manages the input and output of signals and databetween the transmitting unit 11 and the receiving unit 12. Theinterface 103 may manage the input and output of data from and to anapplication not depicted, for example. The receiving unit 12 and thetransmitting unit 11 of the base station 1 depicted in FIG. 2 may beimplemented by a processor that processes wireless signals. Theprocessor that processes wireless signals may be provided separatelyfrom the processor 101.

The wireless communications method performed by a base station may beperformed by the base station depicted in FIG. 2. In the description ofthis example, the wireless communications method performed by a basestation is assumed to be performed by the base station 1 of FIG. 2.

FIG. 5 is a diagram of an example of the wireless communications methodperformed by the base station according to the embodiment. As depictedin FIG. 5, when the wireless communications method is started at thebase station 1, the base station 1 uses the receiving unit 12 to receivefrom the mobile station 2, a wireless signal that includes receptioninformation (step S1). The base station 1 uses the acquiring unit 13 toacquire the reception information from the wireless signal (step S2).

Subsequently, the base station 1 uses the determining unit 14 todetermine for the respective physical channels and based on thereception information, repetition counts for repeated transmission of awireless signal (step S3). The base station 1 acquires from the lookuptable 15, an index value corresponding to the repetition counts for therespective physical channels determined at step S3 (step S4).

Subsequently, the base station 1 uses the transmitting unit 11 totransmit to the mobile station 2, a wireless signal including the indexvalue acquired at step S4 (step S5). As a result, the base station 1notifies the mobile station 2 of the index value. The base station 1then terminates a sequence of the wireless communications method. Thebase station 1 subsequently performs communication through the physicalchannels with the mobile station 2, at the repetition count for eachphysical channel corresponding to the index value in the notification tothe mobile station 2.

According to the wireless communications system depicted in FIG. 1, thebase station 1 depicted in FIG. 2, or the wireless communications methoddepicted in FIG. 5, the base station 1 notifies the mobile station 2 ofthe index value corresponding to the repetition counts of the differentphysical channels. Therefore, as compared to when the base station 1notifies the mobile station 2 of the repetition counts of the differentchannels for each physical channel, the amount of informationtransmitted from the base station 1 to the mobile station 2 is reduced.Thus, the base station 1 can efficiently notify the mobile station 2 ofthe information necessary for signal reception by the mobile station 2.

FIG. 6 is diagram of a functional configuration of a first example ofthe mobile station according to the embodiment. FIG. 7 is a diagram of aflow of signals or data in the mobile station depicted in FIG. 6. Asdepicted in FIGS. 6 and 7, the mobile station 2 has the transmittingunit 21, the receiving unit 22, the generating unit 23, the acquiringunit 24, and the lookup table 25.

The transmitting unit 21 is connected to the generating unit 23 and anantenna 26. The transmitting unit 21 transmits wireless signals from theantenna 26 to the base station 1. The transmitting unit 21 transmitsfrom the antenna 26 to the base station 1, a wireless signal includingreception information generated by the generating unit 23. As a result,the mobile station 2 notifies the base station 1 of the receptioninformation indicating the reception state of the mobile station 2.

The receiving unit 22 is connected to an antenna 27. The receiving unit22 receives via the antenna 27, a wireless signal transmitted from thebase station 1 by using the different physical channels. The receivingunit 22 receives a wireless reference signal via the antenna 27 from thebase station 1. The receiving unit 22 receives via the antenna 27 fromthe base station 1, a wireless signal that includes the index valuecorresponding to the reception information in the notification from thereceiving unit 22.

The generating unit 23 is connected to the receiving unit 22. Thegenerating unit 23 generates based on the wireless reference signalreceived by the receiving unit 22, the reception information indicatingthe reception state of the mobile station 2. The acquiring unit 24 isconnected to the receiving unit 22. The acquiring unit 24 acquires theindex value from the wireless signal received by the receiving unit 22.

In the lookup table 25, the repetition counts of the different physicalchannels are associated with different index values, respectively. Fromthe lookup table 25, the repetition counts corresponding to the indexvalue acquired by the acquiring unit 24 are acquired for each physicalchannel.

Information of the repetition counts for each physical channel acquiredfrom the lookup table 25 is sent from an output terminal 28 connected tothe lookup table 25, to a processing unit that executes a data processbased on the information of the repetition counts for each physicalchannel in the mobile station 2. For example, the information of therepetition counts for each physical channel may be sent from the outputterminal 28 to the transmitting unit 21 or from a signal generating unitgenerating a wireless signal transmitted from the transmitting unit 21.

The hardware configuration of the mobile station 2 is identical to thehardware configuration of the base station 1 depicted in FIG. 4.Therefore, the hardware configuration of the mobile station 2 is notdepicted and will not be described. It is noted that in theconfiguration depicted in FIG. 4, the processor 101 processes a programimplementing a wireless communications method performed by a mobilestation described later. The generating unit 23 and the acquiring unit24 may be implemented in this way in the mobile station 2 depicted inFIG. 6.

The lookup table 25 is retained in the memory 102. The interface 103manages the input and output of signals and data between thetransmitting unit 21 and the receiving unit 22. The transmitting unit 21and the receiving unit 22 of the mobile station 2 depicted in FIG. 6 maybe implemented by a processor that processes wireless signals. Theprocessor that processes wireless signals may be provided separatelyfrom the processor 101.

The wireless communications method performed by a mobile station may beperformed by the mobile station depicted in FIG. 6. In the descriptionof this example, the wireless communications method performed by amobile station is assumed to be performed by the mobile station 2depicted in FIG. 6.

FIG. 8 is a diagram of an example of the wireless communications methodperformed by the mobile station according to the embodiment. As depictedin FIG. 8, when the wireless communications method is started at themobile station 2, the mobile station 2 uses the receiving unit 22 toreceive a wireless reference signal from the base station 1 (step S11).The base station 1 transmits the wireless reference signal before stepS1 in the wireless communications method depicted in FIG. 5.

Subsequently, the mobile station 2 uses the generating unit 23 togenerate reception information indicating the reception state of themobile station 2, based on the received wireless reference signal (stepS12). The mobile station 2 then uses the transmitting unit 21 totransmit the wireless signal including the reception informationgenerated at step S12 to the base station 1 (step S13). As a result, themobile station 2 notifies the base station 1 of the reception state ofthe mobile station 2.

Subsequently, the mobile station 2 uses the receiving unit 22 to receivefrom the base station 1, a wireless signal that includes the index valuecorresponding to the reception information transmitted at step S13 (stepS14). The mobile station 2 uses the acquiring unit 24 to acquire theindex value from the wireless signal (step S15).

Subsequently, for each physical channel, the mobile station 2 acquiresfrom the lookup table 25, repetition counts that correspond to the indexvalue acquired at step S15 (step S16). The mobile station 2 thenterminates a sequence of the wireless communications method. The mobilestation 2 subsequently performs communication through the channels withbase station 1 by using the repetition counts of the respective physicalchannels, corresponding to the index value in the notification from thebase station 1.

According to the mobile station 2 depicted in FIG. 6 or the wirelesscommunications method depicted in FIG. 8, the mobile station 2 notifiedof an index value by the base station 1 can acquire from the lookuptable 25 and for each physical channel, the repetition counts thatcorrespond to the index value. This means that the base station 1suffices to notify the mobile station 2 of an index value instead ofgiving notification of the repetition counts for each channel among thedifferent channels. Therefore, as compared to when the base station 1notifies the mobile station 2 of a repetition count for each channel,the amount of information transmitted from the base station 1 to themobile station 2 is reduced. Thus, the base station 1 can efficientlynotify the mobile station 2 of the information necessary for signalreception by the mobile station 2.

An example of application to an MTC System will be described. Under anenvironment with a low SINR, for example, when a mobile station ispresent in the vicinity of a boundary with an adjacent cell, the SINRmay become lower than the value required for communication between abase station and the mobile station. In such a case, as described above,for example, transmission power may be increased (power boost) ortransmission may be repeated to expand coverage.

FIG. 9 is a diagram of an example of maximum coupling loss betweenuplink and downlink. A table depicted in FIG. 9 is introduced in 3GPP TR36.888 V2.0.2, “Study on provision of low-cost MTC UEs based on LTE.” Inthis table, MCL (Maximum Coupling Loss) stands for a maximum couplingloss. FDD (Frequency Division Duplex) stands for a frequency divisionduplex mode. TDD (Time Division Duplex) stands for a time divisionduplex mode.

In the table depicted in FIG. 9, a UE (User Equipment, mobile station)has one transmission antenna and two reception antennas. Therefore, MCL(FDD, 2×2eNB) represents a maximum coupling loss when communication isperformed in the frequency division duplex mode between an eNB(evolutional Node B, base station) having two transmission antennas andtwo reception antennas and a UE having one transmission antenna and tworeception antennas. MCL (TDD, 8×8eNB) represents a maximum coupling losswhen communication is performed in the time division duplex mode betweenan eNB having eight transmission antennas and eight reception antennasand a UE having one transmission antenna and two reception antennas.

As depicted in FIG. 9, the maximum coupling loss is different for eachof the physical channels. For example, in the example depicted in FIG.9, the maximum coupling loss in the case of the frequency divisionduplex mode is 147.2 dB in PUCCH(1a), 141.7 dB in PRACH, and 140.7 dB inPUSCH. The maximum coupling loss in the case of the frequency divisionduplex mode is 145.4 dB in PDSCH, 149.0 dB in PBCH, 149.3 dB in SCH, and146.1 dB in PDCCH(1A).

As depicted in FIG. 9, the maximum coupling loss differs depending onthe mode of duplex operation. For example, in the example depicted inFIG. 9, the maximum coupling loss in the case of the time divisionduplex mode is 149.4 dB in PUCCH(1a), 146.7 dB in PRACH, and 147.4 dB inPUSCH. The maximum coupling loss in the case of the time division duplexmode is 148.1 dB in PDSCH, 149.0 dB in PBCH, 149.3 dB in SCH, and 146.9dB in PDCCH(1A). The maximum coupling loss MCL is calculated byexpression (1), for example.

MCL=[actual transmission power]−([effective noise power]+[required valueof SINR])

The PUCCH is a physical uplink control channel. The PRACH is a physicalrandom access channel. The PUSCH is a physical uplink shared channel.The PDSCH is a physical downlink shared channel. The PBCH is a physicalbroadcast channel. The SCH is a synchronization channel. The PDCCH is aphysical downlink control channel.

When the current SINR value is smaller than the minimum SINR valuerequired for communication through a physical channel, a coverageexpansion level is required that reduces the difference therebetween tozero. By suitably selecting a level of increase in transmission powerand a transmission repetition count, a required coverage expansion levelcan be satisfied. If a UE is in a coverage hole, the required coverageexpansion level is approximately 0 to 20 dB, for example.

The minimum SINR required for communication through each of the physicalchannels differs with consideration of different reception probabilitiesaccording to the purposes of the physical channels.

The coverage expansion level required for each of the physical channelsis defined as a difference between the current SINR value and theminimum SINR value required for communication through the physicalchannel and is therefore different for each of the physical channels.The difference between the current SINR value and the minimum SINR valuerequired for communication through a physical channel can be eliminatedby increasing the transmission power and/or increasing the transmissionrepetition count for the physical channel. Therefore, the transmissionrepetition count for a physical channel varies depending on thetransmission power for the physical channel. Thus, if a level ofincrease in transmission power for each physical channel is determined,the transmission repetition count satisfying the coverage expansionlevel required for the physical channel is determined for each physicalchannel. It is noted that the values of the maximum coupling loss arenot limited to those depicted in FIG. 9.

FIG. 10 is a diagram of an example of a relation between the repetitioncount and the power boost for the required coverage expansion level. Inthe example depicted in FIG. 10, for example, a physical channel PHYCH1has a required coverage expansion level of 10 dB and a gain of 10 dB maybe achieved by repeating transmission 10 times. For example, a physicalchannel PHYCH2 has a required coverage expansion level of 10 dBidentical to the PHYCH1 and a gain of 6 dB may be acquired by repeatingtransmission four times while a gain of 4 dB is achieved by power boost.

For example, a physical channel PHYCH3 has a required coverage expansionlevel of 12 dB and a gain of 6 dB may be acquired by repeatingtransmission four times while a gain of 6 dB is achieved by power boost.It is noted that the values of the required coverage expansion level,the transmission repetition count, and the power boost are not limitedto those depicted in FIG. 10.

The PHYCH1, the PHYCH2, and the PHYCH3 may be, for example, a PDSCH, aPDCCH, a PHICH, or an EPDCCH. The PHICH is a physical hybrid-ARQindicator channel. The EPDCCH is an enhanced physical downlink controlchannel.

FIG. 11 is a diagram of a functional configuration of a second exampleof the base station according to the embodiment. FIG. 12 is a diagram ofa flow of signals or data in the base station depicted in FIG. 11. Inthis example, description will be taking as an example, a case wherecoverage is expanded for two physical channels, a PDCCH and a PDSCH, inan MTC system.

As depicted in FIGS. 11 and 12, a base station 31 has a radio frequency(RF) receiving unit 32, a cyclic prefix (CP) removing unit 33, and afast Fourier transform (FFT) unit 34. The base station 31 has a PUSCHsignal demodulating unit 35, a determining unit 36, and a lookup table37. The base station 31 has a PDSCH signal generating unit 38, a PDCCHsignal generating unit 39, a PBCH signal generating unit 40, an inversefast Fourier transform (IFFT) unit 41, a CP adding unit 42, and an RFtransmitting unit 43.

The RF receiving unit 32 is connected to an antenna 44. The RF receivingunit 32 receives via the antenna 44, a wireless signal transmitted froma mobile station. The RF receiving unit 32 is an example of a receivingunit.

The CP removing unit 33 is connected to the RF receiving unit 32. The CPremoving unit 33 removes a cyclic prefix from the wireless signalreceived by the RF receiving unit 32. The FFT unit 34 performs fastFourier transform for the signal from which the cyclic prefix is removedby the CP removing unit 33. As a result, a time-domain signal isconverted into a frequency-domain signal.

The PUSCH signal demodulating unit 35 demodulates a PUSCH signalconverted into a frequency-domain signal by the FFT unit 34. The PUSCHsignal demodulating unit 35 demodulates the PUSCH signal and thereby,acquires an SINR value in a notification through the PUSCH signal fromthe mobile station. The SINR value is an example of receptioninformation indicating the reception state of a mobile station. ThePUSCH signal demodulating unit 35 is an example of an acquiring unit.

The determining unit 36 determines transmission repetition counts andpower offset amounts for increasing the transmission power for the PDCCHand the PDSCH, based on the SINR value acquired by the PUSCH signaldemodulating unit 35. The determining unit 36 can determine therepetition counts and the power offset amounts for the physical channelswith a known technique based on the SINR value reported from the mobilestation.

From the lookup table 37, an index value is acquired based on therespective repetition counts and power offset amounts for the PDCCH andthe PDSCH determined by the determining unit 36. The index value iscommon to the PDCCH and the PDSCH. The power offset amount is set forthe PDCCH and the PDSCH, respectively.

The PDSCH signal generating unit 38 generates a PDSCH signal. The PDSCHsignal generating unit 38 generates the PDSCH signal including the indexvalue and the power offset amounts for the PDCCH and the PDSCH. ThePDCCH signal generating unit 39 generates a PDCCH signal. The PBCHsignal generating unit 40 generates a PBCH signal.

The IFFT unit 41 performs inverse fast Fourier transform for the PDSCHsignal generated by the PDSCH signal generating unit 38, the PDCCHsignal generated by the PDCCH signal generating unit 39, or the PBCHsignal generated by the PBCH signal generating unit 40. As a result, afrequency-domain signal is converted into a time-domain signal.

The CP adding unit 42 adds a cyclic prefix to the time-domain signalconverted by the IFFT unit 41. The RF transmitting unit 43 is connectedto the CP adding unit 42 and an antenna 45. The RF transmitting unit 43transmits the wireless signal having the cyclic prefix added by the CPadding unit 42, from the antenna 45 to the mobile station. The RFtransmitting unit 43 is an example of a transmitting unit.

FIG. 13 is a diagram of an example of a lookup table. As depicted inFIG. 13, the lookup table 37 has 16 records corresponding to 16 indexvalues of 0, 1, 2, . . . , 15, for example. For each record, an SINRvalue corresponding to the SINR value in the notification from themobile station is set along with respective repetition count referencevalues and repetition count correction values for the PDSCH and thePDCCH.

In the lookup table 37, the SINR value corresponding to the SINR valuein the notification from the mobile station is preset at theinstallation stage of the base station 31. The SINR value correspondingto the SINR value in the notification from the mobile station isacquired from simulation, for example.

The repetition count reference value is the repetition count when thepower offset amount is 0 dB. In the lookup table 37, the repetitioncount reference values are preset at the installation stage of the basestation 31. The repetition count reference values are acquired fromsimulation, for example. From the repetition count reference values, arecord to be used in FIG. 13 is determined and an index valuecorresponding thereto can be acquired.

The repetition count correction value is a value for correcting therepetition count reference value according to the power offset amount.The repetition count correction value is acquired by, for example,multiplying the repetition count reference value by a correctioncoefficient derived from the power offset amount.

For example, in the example depicted in FIG. 13, when the index value isdenoted by k, a record of an index value k has SINR_(k) set as the SINRvalue corresponding to the SINR value reported by the mobile station. Itis noted that k is an integer from 0 to 15. The record of the indexvalue k has RL_(PDSCH,k) as the repetition count reference value for thePDSCH and RL_(PDCCH,k) as the repetition count reference value for thePDCCH.

The record of the index value k has a calculation expression expressedby, for example, expression (2) set as the repetition count correctionvalue for the PDSCH. The record has a calculation expression expressedby, for example, expression (3) as the repetition count correction valuefor the PDCCH. It is noted that a_(PDSCH) and a_(PDCCH) are correctioncoefficients for the PDSCH and the PDCCH, respectively.

RL _(PDSCH,k) ×a _(PDSCH)  (2)

RL _(PDCCH,k) ×a _(PDCCH)  (3)

When the power offset amount for the PDSCH is denoted by PO_(PDSCH), thecorrection coefficient a_(PDSCH) for the PDSCH is expressed byexpression (4), for example. When the power offset amount for the PDCCHis denoted by PO_(PDCCH), the correction coefficient a_(PDCCH) for thePDCCH is expressed by expression (5), for example.

$\begin{matrix}{a_{PDSCH} = 10^{\frac{- {PO}_{PDSCH}}{10}}} & (4) \\{a_{PDCCH} = 10^{\frac{- {PO}_{PDCCH}}{10}}} & (5)\end{matrix}$

PO_(PDSCH) may take on values of 0 dB, 2 dB, 4 dB, and 6 dB, forexample. PO_(PDCCH) may take on values of 0 dB, 2 dB, 4 dB, and 6 dB,for example. The values that PO_(PDSCH) may take and the values thatPO_(PDCCH) may take may differ.

For example, once the repetition counts and the power offset amounts forthe physical channels are determined by the determining unit 36,repetition count correction values can be obtained for the physicalchannels from the lookup table 37 depicted in FIG. 13 by using therespective power offset amounts and repetition reference values.

The hardware configuration of the base station 31 is the same as thehardware configuration of the base station 1 depicted in FIG. 4.Therefore, the hardware configuration of the base station 31 is notdepicted and redundant description is omitted. It is noted that in theconfiguration depicted in FIG. 4, the processor 101 processes theprogram that implements the wireless communications method performed bythe base station 31. The units 33 to 36, 38 to 42 excluding the RFreceiving unit 32 and the RF transmitting unit 43 may be implemented inthis way at the base station 31 depicted in FIG. 11.

The lookup table 37 is retained in the memory 102. The interface 103manages the input and output of signals and data between the RFtransmitting unit 43 and the RF receiving unit 32. The RF transmittingunit 43 and the RF receiving unit 32 of the base station 31 depicted inFIG. 11 may be implemented by a processor that processes wirelesssignals. The processor that processes wireless signals may be providedseparately from the processor 101.

The wireless communications method performed by the base station 31 isidentical to the method depicted in FIG. 5, for example. Therefore,redundant description of the method is omitted. It is noted that in themethod depicted in FIG. 5, the reception information is the SINR value.At step S3, the base station 31 uses the determining unit 36 todetermine the repetition counts and the power offset amounts. At stepS5, the base station 31 uses the RF transmitting unit 43 to transmit thewireless signal including the index value and the power offset amountsto the mobile station.

According to the base station 31 depicted in FIG. 11, the base station31 notifies the mobile station of an index value common to therepetition counts of the different physical channels. Therefore, ascompared to when the base station 31 notifies the mobile station of therepetition counts for each physical channel among the differentchannels, the amount of information sent from the base station 31 to themobile station is reduced. Thus, the base station 31 can efficientlynotify the mobile station of the information necessary for signalreception by the mobile station.

According to the base station 31 depicted in FIG. 11, the base station31 notifies the mobile station of the power offset amount for eachchannel. This enables the mobile station to obtain the repetition countsof the respective physical channels, based on the index value common tothe different physical channels and the power offset amount for eachphysical channel.

According to the base station 31 depicted in FIG. 11, the repetitioncount can be corrected according to the power offset amount based on acalculation expression set in the lookup table 37. Additionally, theindex value can be easily acquired by finding the index value for whichthe repetition count correction values obtained by using the lookuptable 37 matches the repetition counts determined based on the SINRvalue in the notification from the mobile station. Moreover, in thelookup table 37, since the SINR value and the repetition count referencevalue are acquired by, for example, simulation, the lookup table 37 canbe easily created.

FIG. 14 is a diagram of a functional configuration of a second exampleof the mobile station according to the embodiment. FIG. 15 is a diagramof a flow of signals or data in the base station depicted in FIG. 14. Inthis example, description will be taken as an example, a case wherecoverage is expanded for two physical channels, a PDCCH and a PDSCH, inan MTC system.

As depicted in FIGS. 14 and 15, the mobile station 51 has an RFreceiving unit 52, a CP removing unit 53, and an FFT unit 54. The mobilestation 51 has a PDSCH signal demodulating unit 55, a PDCCH signaldemodulating unit 56, a reference signal demodulating unit 57, a PBCHsignal demodulating unit 58, a lookup table 59, and a SINR calculatingunit 60. The mobile station 51 has an RF transmitting unit 61, a CPadding unit 62, an IFFT unit 63, a PRACH signal generating unit 64, aPUSCH signal generating unit 65, and a user data buffer 66.

The RF receiving unit 52 is connected to an antenna 67. The RF receivingunit 52 receives via the antenna 67, a wireless signal transmitted froma base station. The RF receiving unit 52 is an example of a receivingunit.

The CP removing unit 53 is connected to the RF receiving unit 52. The CPremoving unit 53 removes a cyclic prefix from the wireless signalreceived by the RF receiving unit 52. The FFT unit 54 performs fastFourier transform for the signal from which the cyclic prefix is removedby the CP removing unit 53. As a result, a time-domain signal isconverted into a frequency-domain signal.

The PDSCH signal demodulating unit 55 demodulates a PDSCH signalconverted into a frequency-domain signal by the FFT unit 54. The PDSCHsignal demodulating unit 55 demodulates the PUSCH signal and thereby,acquires an index value and a power offset amount in a notificationthrough a PDSCH signal from the base station. The PDSCH signaldemodulating unit 55 is an example of an acquiring unit.

The PDCCH signal demodulating unit 56 demodulates a PDCCH signalconverted into a frequency-domain signal by the FFT unit 54. Thereference signal demodulating unit 57 demodulates a reference signalconverted into a frequency-domain signal by the FFT unit 54. The PBCHsignal demodulating unit 58 demodulates a PBCH signal converted into afrequency-domain signal by the FFT unit 54.

From the lookup table 59, the repetition count for the PDSCHcorresponding to the power offset amount for the PDSCH is acquired basedon the index value and the power offset amount for the PDSCH acquired bythe PDSCH signal demodulating unit 55. Additionally, from the lookuptable 59, the repetition count for the PDSCH corresponding to the poweroffset amount for the PDSCH is acquired based on the index value and thepower offset amount for the PDSCH acquired by the PDSCH signaldemodulating unit 55. The lookup table 59 may be the same table as thelookup table 37 depicted in FIG. 13.

The information of the repetition counts of the respective physicalchannels acquired from the lookup table 59 and the respective poweroffset amounts of the physical channels is sent from an output terminal69 connected to the lookup table 59, to a processing unit that executesa data process based on this information at the mobile station 51.

For example, the information of the repetition count and the poweroffset amount for the PDSCH is sent to the PDSCH signal demodulatingunit 55. The PDSCH signal demodulating unit 55 demodulates the PDSCHsignal based on the information of the repetition count and the poweroffset amount for the PDSCH. The information of the repetition count andthe power offset amount for the PDCCH is sent to the PDCCH signaldemodulating unit 56. The PDCCH signal demodulating unit 56 demodulatesthe PDCCH signal based on the information of the repetition count andthe power offset amount for the PDCCH.

As is the case with the PDSCH and the PDCCH, the information of therespective repetition counts and power offset amounts is acquired forthe PRACH and the PUSCH. For example, the information of the repetitioncount and the power offset amount for the PRACH is sent to the PRACHsignal generating unit 64. The PRACH signal generating unit 64 generatesthe PRACH signal based on the information of the repetition count andthe power offset amount for the PRACH. The information of the repetitioncount and the power offset amount for the PUSCH is sent to the PUSCHsignal generating unit 65. The PUSCH signal generating unit 65 generatesthe PUSCH signal based on the information of the repetition count andthe power offset amount for the PUSCH.

The SINR calculating unit 60 calculates an SINR value based on thereception intensity of the reference signal demodulated by the referencesignal demodulating unit 57. The SINR calculating unit 60 can calculatethe SINR value by a known technique based on the reception intensity ofthe reference signal. The SINR value is an example of the receptioninformation indicating the reception state of the mobile station 51. TheSINR calculating unit 60 is an example of a generating unit.

The user data buffer 66 temporarily retains the SINR value acquired bythe SINR calculating unit 60. The PUSCH signal generating unit 65generates a PUSCH signal including the SINR value stored in the userdata buffer 66. The PRACH signal generating unit 64 generates a PRACHsignal.

The IFFT unit 63 performs inverse fast Fourier transform for the PRACHsignal generated by the PRACH signal generating unit 64 or the PUSCHsignal generated by the PUSCH signal generating unit 65. As a result, afrequency-domain signal is converted into a time-domain signal.

The CP adding unit 62 adds a cyclic prefix to the time-domain signalconverted by the IFFT unit 63. The RF transmitting unit 61 is connectedto the CP adding unit 62 and an antenna 68. The RF transmitting unit 61transmits from the antenna 68 to the base station, the wireless signalhaving the cyclic prefix added by the CP adding unit 62. The RFtransmitting unit 61 is an example of a transmitting unit.

The hardware configuration of the mobile station 51 is identical to thehardware configuration of the base station 1 depicted in FIG. 4.Therefore, the hardware configuration of the mobile station 51 is notdepicted and redundant description is omitted. It is noted that in theconfiguration depicted in FIG. 4, the processor 101 processes theprogram implementing the wireless communications method performed by themobile station 51. The units 53 to 58, 60, 62 to 65 except the RFreceiving unit 52 and the RF transmitting unit 61 may be implemented inthis way in the mobile station 51 depicted in FIG. 14.

The lookup table 59 is retained in the memory 102. The user data buffer66 may be implemented by the memory 102. The interface 103 manages inputand output of signals and data between the RF transmitting unit 61 andthe RF receiving unit 52. The RF transmitting unit 61 and the RFreceiving unit 52 of the mobile station 51 depicted in FIG. 14 may beimplemented by a processor processing a wireless signal. The processorprocessing a wireless signal may be provided separately from theprocessor 101.

The wireless communications method performed by the mobile station 51 isidentical to the method depicted in FIG. 8, for example. Therefore,redundant description of the method is omitted. It is noted that in themethod depicted in FIG. 8, the wireless reference signal is thereference signal and that the reception information is the SINR value.At step S14, the mobile station 51 receives the wireless signalincluding the index value and the power offset amounts of the respectivechannels.

According to the mobile station 51 depicted in FIG. 14, when notified ofthe index value from the base station, the mobile station 51 can acquirefor the respective physical channels from the lookup table 59, therepetition counts corresponding to the index value. This means that thebase station can notify the mobile station 51 of the index value insteadof giving notification of the repetition counts for each physicalchannel among the different physical channels. Therefore, as compared towhen the base station notifies the mobile station 51 of repetitioncounts for each physical channel, the amount of information sent fromthe base station to the mobile station 51 is reduced. As a result, thebase station can efficiently notify the mobile station 51 of theinformation necessary for signal reception by the mobile station 51.

According to the mobile station 51 depicted in FIG. 14, the base stationnotifies the mobile station 51 of the respective power offset amountsfor the physical channels. This enables the mobile station 51 to obtainthe respective repetition counts of the physical channels based on theindex value common to the different physical channels and the respectivepower offset amounts of the physical channels.

According to the mobile station 51 depicted in FIG. 14, the repetitioncount can be corrected according to the power offset amount, based on acalculation expression set in the lookup table 59 for each index value.Additionally, since the repetition count reference value in the lookuptable 59 is acquired by, for example, simulation, the lookup table 59can be easily created.

FIG. 16 is a diagram of an example of a wireless connection processsequence in a wireless communications system according to theembodiment. As depicted in FIG. 16, it is assumed that the wirelesscommunications system includes a base station, a mobile station A, and amobile station B. The mobile station A and the mobile station B may haverequired coverage expansion levels different from each other. Forexample, the coverage expansion level required for the mobile station Amay be 15 dB and the coverage expansion level required for the mobilestation B may be 20 dB.

When the wireless connection process is started, first, the base stationtransmits synchronization signals to the mobile station A and the mobilestation B (step S21). Subsequently, the base station uses the PBCHsignals to transmit system information, SIB (system information block),to the mobile station A and the mobile station B. At this point in time,the base station does not know the coverage expansion levels requiredfor the mobile station A or the mobile station B and therefore,transmits the PBCH signals at the maximum repetition count (step S22).

Subsequently, the mobile station A and the mobile station B transmit thePRACH signals to the base station at the maximum repetition count (stepS23). Subsequently, the base station transmits cell-specific referencesignals (CRSs) to the mobile station A and the mobile station B (stepS24). The mobile station A and the mobile station B receive thereference signals and then calculate the SINR values to roughlydetermine the coverage expansion levels (step S25). The base stationtransmits the PDCCH signals to the mobile station A and the mobilestation B at the maximum repetition count (step S26).

Subsequently, the mobile station A and the mobile station B transmit thePUSCH signals including the SINR values to the base station at themaximum repetition count to feed back the SINR values to the basestation (step S27). The base station receives the PUSCH signalsincluding the SINR values and then determines the repetition counts andthe power offset amounts for channels, for example, the PDCCH and thePDSCH, based on the SINR values (step S28).

Subsequently, the base station acquires from the lookup table, an indexvalue common to the channels and power offset values for the respectivechannels. The base station transmits the PDSCH signals including theindex value to the mobile station A and the mobile station B to notifythe mobile station A and the mobile station B of the index value (stepS29). The base station transmits the PDSCH signals including the poweroffset amounts of the respective channels to the mobile station A andthe mobile station B to notify the mobile station A and the mobilestation B of the respective power offset amounts of the channels (stepS30).

The mobile station A and the mobile station B acquire the respectiverepetition counts of the channels from the lookup tables, based on theindex value and the power offset amounts. Subsequently, communicationlinks are maintained between the base station and the mobile stations A,B based on the repetition counts of the respective channels and thepower offset amounts of the respective channels.

A reduction in the amount of information sent from the base station tothe mobile station will be described. FIG. 17 is a diagram of an exampleof a sequence of notification of an index value common to channels. FIG.18 is an example of a sequence of notification of respective repetitioncounts for the channels. In the examples depicted in FIG. 17 and FIG.18, it is assumed that physical channels PHYCH1, PHYCH2, PHYCH3, andPHYCH4 exist.

As depicted in FIG. 17, in the case of notification of an index valuecommon to the channels, a base station transmits a PDSCH signalincluding the index value to a mobile station (step S41). The basestation transmits a PDSCH signal including a power offset amount for thePHYCH1 to the mobile station (step S42). The base station transmits aPDSCH signal including a power offset amount for the PHYCH2 to themobile station (step S43). The base station transmits a PDSCH signalincluding a power offset amount for the PHYCH3 to the mobile station(step S44). The base station transmits a PDSCH signal including a poweroffset amount for the PHYCH4 to the mobile station (step S45).

On the other hand, as depicted in FIG. 18, in the case of notificationof the respective repetition counts for the channels, the base stationtransmits a PDSCH signal including the repetition count for the PHYCH1to the mobile station (step S51). The base station transmits a PDSCHsignal including the repetition count for the PHYCH2 to the mobilestation (step S52). The base station transmits a PDSCH signal includingthe repetition count for the PHYCH3 to the mobile station (step S53).The base station transmits a PDSCH signal including the repetition countfor the PHYCH4 to the mobile station (step S54).

Additionally, the base station transmits a PDSCH signal including apower offset amount for the PHYCH1 to the mobile station (step S55). Thebase station transmits a PDSCH signal including a power offset amountfor the PHYCH2 to the mobile station (step S56). The base stationtransmits a PDSCH signal including a power offset amount for the PHYCH3to the mobile station (step S57). The base station transmits a PDSCHsignal including a power offset amount for the PHYCH4 to the mobilestation (step S58).

In the examples depicted in FIG. 17 and FIG. 18, for example, the poweroffset amount is assumed to be any of four values of 0 dB, 2 dB, 4 dB, 6dB and the repetition count is assumed to be any of 1, 2, . . . , 15,and 16. The index value is assumed to be any of 0, 1, . . . , 14, and15. In this case, the base station requires an information amount of twobits for notifying the mobile station of a power offset amount. The basestation requires an information amount of four bits for notifying themobile station of a repetition count. The base station requires aninformation amount of four bits for notifying the mobile station of anindex value.

Therefore, in the case of notification of the index value depicted inFIG. 17, since four bits are required for the notification of the indexvalue and eight bits are required for the notification of the poweroffset amounts of the four channels, a total of 12 bits are required. Incontrast, in the case of notification of the repetition counts for therespective channels depicted in FIG. 18, since 16 bits are required fornotification of the repetition counts of the four channels and eightbits are required for the notification of the power offset amounts ofthe four channels, a total of 24 bits are required.

Therefore, the notification of the index value reduces the number ofbits required for notification by half as compared to the case ofnotification of the repetition counts for each channel. If the number ofchannels further increases, the number of bits required for notificationof the index value does not change while the number of required bitsincreases in the case of notification of the repetition counts for eachchannel and therefore, the sufficient number of bits required fornotification of the index value is equal to or less than a half of thenumber of bits required for notification of the repetition counts foreach channel. As described above, the notification of the index valuecan reduce the number of bits required for notification as compared tothe case of notification of the repetition counts for each channel.

Although a terminal that wirelessly communicates with a base station isa mobile station in the examples described above, the terminal may befixed at a certain position without moving.

The base station, the mobile station, the wireless communicationssystem, and the wireless communications method provide an effect that abase station can efficiently notify a mobile station of informationnecessary for signal reception.

All examples and conditional language provided herein are intended forpedagogical purposes of aiding the reader in understanding the inventionand the concepts contributed by the inventor to further the art, and arenot to be construed as limitations to such specifically recited examplesand conditions, nor does the organization of such examples in thespecification relate to a showing of the superiority and inferiority ofthe invention. Although one or more embodiments of the present inventionhave been described in detail, it should be understood that the variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A base station comprising: a transmitting circuitthat transmits a first wireless signal to a mobile station by using aplurality of different physical channels; a receiving circuit thatreceives a second wireless signal transmitted from the mobile station;an acquiring circuit that acquires reception information indicating areception state of the first wireless signal at the mobile station, fromthe second wireless signal received by the receiving circuit; adetermining circuit that based on the reception information acquired bythe acquiring circuit, determines a repetition count of a third wirelesssignal repeatedly transmitted from the transmitting circuit; and alookup table that has an index value associated with repetition counts,wherein the base station uses the receiving circuit to receive thesecond wireless signal from the mobile station, the base station usesthe acquiring circuit to acquire the reception information, the basestation uses the determining circuit to determine based on the receptioninformation, the repetition count for each physical channel among theplurality of different physical channels, the base station acquires fromthe lookup table, the index value that corresponds to the repetitioncounts of the plurality of different physical channels, and the basestation uses the transmitting circuit to transmit a fourth wirelesssignal that includes the index value, to the mobile station and notifythe mobile station of the index value.
 2. The base station according toclaim 1, wherein the base station uses the determining circuit todetermine based on the reception information, a power offset amount forchanging a transmission power, and the base station uses thetransmitting circuit to transmit a fifth wireless signal that includesthe power offset amount, to the mobile station and notify the mobilestation of the power offset amount.
 3. The base station according toclaim 2, wherein the lookup table, for each index value among aplurality of different index values, has for each plurality of differentphysical channels, a value corresponding to the reception information,reference values of the repetition counts, and calculation expressionsfor correcting the reference values based on the power offset amount. 4.The base station according to claim 3, wherein the base station acquiresfrom the lookup table, an index value for which values derived from thecalculation expressions based on the power offset amount and thereference values match the repetition counts determined by thedetermining circuit.
 5. The base station according to claim 3, whereinthe value corresponding to the reception information and the referencevalues are obtained in advance by simulation.
 6. A mobile stationcomprising: a transmitting circuit that transmits a first wirelesssignal to a base station; a receiving circuit that receives a secondwireless signal transmitted from the base station by using a pluralityof different physical channels, a generating circuit that generatesreception information indicating a reception state based on the secondwireless signal received by the receiving circuit; an acquiring circuitthat acquires an index value from the second wireless signal received bythe receiving circuit; a lookup table having associated with the indexvalue among a plurality of different index values, repetition counts ofa third wireless signal repeatedly transmitted from the base station byusing the plurality of different physical channels, wherein the mobilestation uses the receiving circuit to receive a wireless referencesignal from the base station, the mobile station uses the generatingcircuit to generate the reception information based on the wirelessreference signal, the mobile station uses the transmitting circuit totransmit the first wireless signal including the reception information,to the base station and notify the base station of the receptioninformation, the mobile station uses the receiving circuit to receivefrom the base station, a fourth wireless signal that includes the indexvalue corresponding to the reception information, the mobile stationuses the acquiring circuit to acquire the index value from the fourthwireless signal that includes the index value, and the mobile stationacquires for the plurality of different physical channels from thelookup table, the repetition counts corresponding to the index value. 7.The mobile station according to claim 6, wherein the mobile station usesthe receiving circuit to receive from the base station, a fifth wirelesssignal that includes a power offset amount for changing a transmissionpower of the base station, the mobile station uses the acquiring circuitto acquire the power offset amount from the fifth wireless signal thatincludes the power offset amount, and the mobile station acquires forthe plurality of different physical channels from the lookup table, therepetition counts corresponding to the power offset amount.
 8. Themobile station according to claim 7, wherein the lookup table, for eachindex value among a plurality of different index values, has for eachplurality of different physical channels, a value corresponding to thereception information, reference values of the repetition counts, andcalculation expressions for correcting the reference values based on thepower offset amount.
 9. The mobile station according to claim 8, whereinthe reference values are obtained in advance by simulation.
 10. Awireless communications system comprising: a base station and a mobilestation, wherein the base station includes: a base-station transmittingcircuit that transmits a first wireless signal to the mobile station byusing a plurality of different physical channels; a base-stationreceiving circuit that receives a second wireless signal transmittedfrom the mobile station; a base-station acquiring circuit that acquiresreception information indicating a reception state of the first wirelesssignal at the mobile station, from the second wireless signal receivedby the base-station receiving circuit; a determining circuit that basedon the reception information acquired by the base-station acquiringcircuit, determines a repetition count of a third wireless signalrepeatedly transmitted from the base-station transmitting circuit; and abase-station lookup table that has an index value associated withrepetition counts, the base station uses the base-station receivingcircuit to receive the second wireless signal from the mobile station,the base station uses the base-station acquiring circuit to acquire thereception information, the base station uses the determining circuit todetermine, based on the reception information, the repetition count foreach physical channel among the plurality of different physicalchannels, the base station acquires from the base-station lookup table,the index value that corresponds to the repetition counts of theplurality of different physical channels, the base station uses thebase-station transmitting circuit to transmit a fourth wireless signalthat includes the index value, to the mobile station and notify themobile station of the index value, the mobile station includes: amobile-station transmitting circuit that transmits the second wirelesssignal to the base station; a mobile-station receiving circuit thatreceives the first wireless signal transmitted from the base station byusing the plurality of different physical channels, a generating circuitthat generates the reception information indicating the reception statebased on the first wireless signal received by the mobile-stationreceiving circuit; a mobile-station acquiring circuit that acquires theindex value from the fourth wireless signal received by themobile-station receiving circuit; a mobile-station lookup table havingassociated with each index value among the plurality of different indexvalues, the repetition counts of the third wireless signal repeatedlytransmitted from the base station by using the plurality of differentphysical channels, the mobile station uses the mobile-station receivingcircuit to receive a wireless reference signal from the base station,the mobile station uses the generating circuit to generate the receptioninformation based on the wireless reference signal, the mobile stationuses the mobile-station transmitting circuit to transmit the secondwireless signal including the reception information, to the base stationand notify the base station of the reception information, the mobilestation uses the mobile-station receiving circuit to receive from thebase station, the fourth wireless signal that includes the index valuecorresponding to the reception information, the mobile station uses themobile-station acquiring circuit to acquire the index value from thefourth wireless signal that includes the index value, and the mobilestation acquires for the plurality of different physical channels fromthe mobile-station lookup table, the repetition counts corresponding tothe index value.
 11. A wireless communications method comprising:receiving from a mobile station, a first wireless signal that includesreception information indicating a reception state of a second wirelesssignal at the mobile station; acquiring the reception information fromthe first wireless signal that includes the reception information;determining for the plurality of different physical channels and basedon the reception information, repetition counts of a third wirelesssignal repeatedly transmitted; acquiring from a lookup table havingassociated with each index value among a plurality of different indexvalues, repetition counts of each plurality of different physicalchannels, an index value that corresponds to the repetition counts ofthe plurality of different physical channels; and transmitting a fourthwireless signal that includes the index value, to the mobile station andnotifying the mobile station of the index value, wherein the wirelesscommunications method is performed by a base station.
 12. A wirelesscommunications method comprising: receiving a wireless reference signalfrom a base station; generating reception information indicating areception state based on the wireless reference signal; transmitting afirst wireless signal that includes the reception information, to thebase station and notifying the base station of the receptioninformation; receiving from the base station, a second wireless signalthat includes an index value corresponding to the reception information;acquiring the index value from the second wireless signal; acquiring fora plurality of different physical channels from a lookup table havingassociated with each index value among a plurality of different indexvalues, repetition counts of a third wireless signal repeatedlytransmitted from the base station by using the plurality of differentphysical channels, the repetition counts corresponding to the indexvalue, wherein the wireless communications method is performed by amobile station.